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# 协议(License)：署名-非商业性使用-相同方式共享 4.0 国际 (CC BY-NC-SA 4.0)
# 作者(Author)：
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# 来源(Source)：

#include<bits/stdc++.h>
#define ios ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0)
#define debug  freopen("in.txt","r",stdin),freopen("out.txt","w",stdout);
#define fs first
#define sc second
#define pb push_back
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int maxn = 1e6+10;
using namespace std;
 
string s,t;
int main(){
    // debug;
    ios;
    cin>>s>>t;
    int lens = s.length(),lent = t.length();
    if(lens+1 == lent && s == t.substr(0,lent-1))
        cout<<"Yes\n";
    else
        cout<<"No\n";
    return 0;
}
